Various proposals exist in the art for insertion of slats between the cords of the cross-rungs running between two side cords of a venetian blind ladder cord (or the like). These proposals have usually involved some form of spreader which pulls the side cords apart and have generally included a guide which enables the slat material to be slid into place. Furthermore, some of the proposals involved angling the rungs with respect to the leading edge of the slat in order to facilitate entry of the leading edge of each slat between individual cords of a cross-rung.
Unfortunately, the spreaders known to the art have generally been unable to provide an optimal opening, i.e. the so-called "target," between the spread apart cords of a so called active cross-rung at the point where the slat is being inserted.
However, one proposal, disclosed in pending U.S. patent application entitled "Unit for Positioning a Venetian Blind Ladder and for Guiding the Slats of the Blind Thereonto", Ser. No 506,352, filed June 21, 1983 solves many of the problems associated with prior art spreaders. As described therein, a pair of adjacent cords are spread apart by means of a rotating pawl an an abutment plate carried by a torsion bar. The pawl exerts a downward force on a lower non-active rung, while the abutment surface exerts an upward force on the active cross-rung. Each slat is supported by a number of stops, each of which moves along a curved (arc-shaped) path. While this arrangement solves many of the problems associated with prior art designs and is thus perfectly satisfactory for inserting slats in ladder cords having a fairly wide spacing, this arrangement, due to the arc-shaped motion of the stops, may in some instances be susceptible to dumping a heavy slat load or performing incorrectly--particularly where the dimensional tolerances between the ladder cord and the slat are small, e.g. where close control ladder cords are used.